In some very high tension units such as the one outlined in FIG. 1, there are outgoing conductors 3 and 4 between a first set of bars 1 and a second set of bars 2, conductors 3 and 4 being protected by circuit-breakers 5, 6 and 7.
The outgoing conductors are surrounded by current transformers such as 8 and 9 for outgoing conductor 3 and 10 and 11 for outgoing conductor 4. The outgoing conductors can be either cable terminals such as the one referenced 3A in FIG. 2 which illustrates an embodiment of the portion G encircled in FIG. 1, or an aerial conductor which, like the one referenced 3B and illustrated by broken lines, runs vertically to the link line between the two transformers 8 and 9 and then runs parallel to the link line.
For a three-phase unit and a plurality of outgoing and in-coming conductors, this disposition occupies a great deal of space, either vertically or horizontally. Now, there is an increasing demand for very high tension electric units which are as compact as possible with respect to surface area and volume.
In current transformers the most expensive and least compact part with respect to floor area is the insulation.
Preferred embodiments of the invention provide measuring apparatus which performs the functions of two current transformers in the form of a single unit for insulation from the earth.